The invention concerns a radial piston pump, with a pump housing, which possesses a plurality of cylindrical bores for the reception of pistons, the bores being arrayed in a star-shape around a cam, and the pump further possessing intake and outlet openings which penetrate to the inner chamber of each cylinder and thus to the compressed working volume therein.
The pistons in the pump housing, which is designed as a stationary cylinder block, are displaced by the rotating cam mounted on the drive shaft. The flow of pressurized medium in the pump, as a rule, is controlled by suction and pressure valves. Another pump concept operates by means of intake suction slots and with valving on the pressure side, similar to that mentioned above.
Radial piston pumps of the above mentioned method of construction are well known in the current state of the technology. One disadvantage of the known radial piston pumps is the noise, since upon the conveyance of a pressure medium, a strong pressure impulse occurs in the inner chamber of the piston, which generates a generally unpleasantly loud noise. By such an abrupt pressure stroke, a steep gradient with a high pressure peak is produced, which exceeds the allowable output pressure in the plenum chamber of the pump by several times. These impact pressures increase themselves as a matter of principle with increasing speed of rotation. The pressure impact of all pistons generate the noise level, which then emanates from the housing wall as air borne noise. For the solution of this problem, a multiplicity of different proposals within the state of the technology have been made known.
For instance, in this direction, a proposal has been made to the effect that the pump housing be provided with an insulating coating or even, in another way, be encapsulated against noise. The necessary monetary and space requirements are substantial.
DE 42 41 825 A1 contends, as a fundamental measure, that the noise essentially forms at those points where very high pressures occur and thus sharp force gradients are generated. Since these gradients appear especially at the base of the piston, this proposal suggests that by the intentional implantation of elasticity at the piston, that is, more precisely, at the connection between the piston and the pin bearing, both the force gradients and the noise intensity will be diminished.
DE 43 36 673 C2 describes a pump, the main feature of which contends, that between the piston and the slide elements which are on the contact surface of the eccentric cam, an annular spring can be installed which encircles the cam. The pistons then springingly abut the cam, so that at the start of their outward sliding movement, the pistons can have any abrupt cam impulse ameliorated by the spring, thus diminishing the pressure peaks.
A further solution to the problem of diminishing the pump noise is described in DE 44 25 929 A1. This proposal is based on a premise, that the pistons are to be provided with compensating pressure, an additional oil source, which is in communication with a circumferential conduit. By this means, each piston receives a modifying intake of oil from the compensation space, so that uniform pressure chamber filling can take place with a minimum amount of noise.
Since, however, these above mentioned designs of the radial piston pumps have not resulted in the expected noise reduction with reasonable manufacturing costs, it is the purpose of the present invention to make available a radial piston pump which, particularly during a compression stroke of the piston, reduces the pressure gradients within the inner cylinder chamber, and thus makes the pump quieter.
This purpose is achieved by a radial piston pump having the features of claim 1 while advantageous embodiments are to be found in the subsequent subordinate claims.
The main feature of the new kind of pump is now found therein, in accord with the invention, that the compressible working volume is connectable to a space of lesser pressure by means of at least one relief opening. By this means, the pressure gradient in the cylinder inner chamber, during the compressing stroke of the piston, is immediately modified even as it originates, and thus, a significant noise reduction of the pump is advantageously achieved. The number of the cylinders of a pump, so equipped with a relief valve, is dependent upon the current demands of the application. Preferably, every cylinder should be equipped with at least one such relief opening.
An advantageous embodiment of the invention is the construction of a chamfer on the forward edge of the piston, which coacts with the inlet opening. This chamfer can be formed around the entire circumference of the piston, or only at that part which coacts with the inlet opening. As a compression stroke proceeds, the piston moves over the inlet opening and tightly closes the same. As the compression stroke continues, the medium enclosed within the cylinder interior compresses itself as the working volume.
The chamfer on the piston prevents, at this point, a too sudden an increase in pressure in the cylinder interior, since between the inlet opening and the now tapered rim-section of the piston, the pressure medium, for a short instant, can back flow into a space of lesser pressure located at the outer approach to the inlet opening. By this means, the pressure peaking in the cylinder inner chamber is rounded off.
In a particular development of the invention, provisions have been made so that the inlet opening is designed as an inlet window to the inner chamber of the cylinder, whereby the side which lies radially outward therefrom is commonly designated as the control side. xe2x80x9cRadialxe2x80x9d in this connection refers to the axis of rotation of the radial piston pump. In one embodiment in accord with the invention, the relief opening, is located radially outside of the control side of the inlet window in the pump housing.
This permits the relief opening to be at a greater distance from the axis of rotation of the pump than is the inlet control side, and also allows the relief procedure to begin immediately after the closure of the inlet window by the piston.
The relief opening can be placed in the cylindrical bore at any optional, technically sound position. However, it is particularly recommended that the (at least) one relief opening be placed diametrically opposite to the inlet window in the cylindrical bore. Thereby a spatial separation is advantageously achieved between the suction side of the inlet window and the pressure side located relief opening, which offers a substantial reduction of the pressure gradient.
The relief opening in one embodiment, can be so designed so that essentially it exhibits a mirror image symmetry, whereby the plane of symmetry runs principally perpendicular to the longitudinal axis of the cylinder. The relief opening is then designed as one or more bores, or a slot, or lenticular or the like, wherein the longitudinal axis, for instance that of a slot or the lens, is essentially aligned in the direction of the cylinder axis.
In another particular development, the proposal is made that the relief opening possess an open cross section which is tapered by a narrowing toward the outside. Such a relief may be constructed in the form of a triangle, wherein the apex of the triangle points away from the rotational axis of the pump and toward the outside. Since, at the start of the compression, which coincides with the beginning of the buildup of the pressure gradient, and at the time when the greatest quantity of oil is available in the cylinder interior, then, due to the shape of the relief opening, it is advantageously achieved, that initially a large quantity of oil can escape through the xe2x80x9clargexe2x80x9d part of the relief opening, i.e. the xe2x80x9cbasexe2x80x9d of the triangle. As the operational stroke of the piston continues, then the available open cross-section for the relief diminishes since, at this point in time, the oil volume in the cylinder inner chamber has already been reduced.
In the following, additional shapes of the relief openings are described, which shapes generally correspond to the outline of a triangle. To accomplish its purpose, the relief opening can, for instance, be comprised of three bores, which are so disposed that the middle points thereof form a triangle.
In a particularly advantageous design of the invention, proposed is, that the relief opening be comprised of two relief opening bores, radially offset one from the other, wherein the radially outward situated bore has a smaller diameter than the inner situated bore. Such a relief opening is technically simple to achieve and is a low cost part of the manufacture. The bores are, in an advantageous manner, drilled in the cylinder wall of the pump housing essentially perpendicular to the longitudinal axis of the cylinder.
The radial distance between the centers of these two relief bores represents approximately a one to three fold diameter of the bore itself so that these bores are placed relatively close to one another. The effect of pressure relief of such located bores corresponds to that of a relief opening with an opening surface, the cross-section of which narrows toward the outside, as this has already been described in the case of a triangular opening.
The relief opening, however, is normally so designed that it exhibits a constant opening. Alternatively, the relief opening can be designed as an orifice with a variable flow opening, so that, for example, a temperature dependent adjustment of the relief opening becomes possible.
A further proposal is, that the relief openings be connected with one another by a circumferentially running annular conduit. By this means the achievement is that the pressure medium exiting from the cylinders, through the relief openings, can be captured and can be utilized once again in the process. The annular conduit can alternatively be provided on the intake side in a connection housing.
In a further development of the invention, the proposal is, that an annular conduit be placed in a separate flange ring. For this purpose, the annular conduit can be manufactured simply and economically as a separate component possibly by machining.
The flange ring would subsequently be pushed onto a connection means on the pump housing on that side of the housing opposite to the suction side.